A position sensor can detect the presence and location of a touch by a finger or by an object, such as a stylus, within an area of an external interface of the position sensor. In a touch sensitive display application, the position sensor enables, in some circumstances, direct interaction with information displayed on the screen rather than indirectly via a mouse or touchpad. Position sensors can be attached to or provided as part of devices with a display. Examples of displays include, but are not limited to, computers, personal digital assistants (PDAs), satellite navigation devices, mobile telephones, portable media players, portable game consoles, public information kiosks, and point of sale systems. Position sensors have also been used as control panels on various appliances.
There are a number of different types of position sensors. Examples include, but are not limited to, resistive touch screens, surface acoustic wave touch screens, capacitive touch screens, and the like. A capacitive touch screen, for example, may include an insulator coated with a transparent conductor in a particular pattern. When an object, such as a finger or a stylus, touches the surface of the screen there is a change in capacitance. This change in capacitance is sent to a controller for processing to determine the position where the touch occurred.
In a mutual capacitance configuration, for example, an array of conductive drive electrodes or lines and conductive sense electrodes or lines can be used to form a touch screen having capacitive nodes. A node may be formed at each intersection of a drive electrode and a sense electrode. The electrodes cross at the intersections but are separated by an insulator so as to not make electrical contact. In this way, the sense electrodes are capacitively coupled with the drive electrodes at the intersection nodes. A pulsed or alternating voltage applied on a drive electrode will therefore induce a charge on the sense electrodes that intersect with the drive electrode. The amount of induced charge is susceptible to external influence, such as from the proximity of a nearby finger. When an object approaches the surface of the screen, the capacitance change at every individual node on the grid can be measured to determine the location or position of the object.